Embolization involves the partial or complete occlusion of blood vessels, limiting the flow of blood therethrough. The intentional occlusion of blood vessels (“therapeutic embolization”) may be used to treat a variety of vascular and non-vascular conditions including cerebral and peripheral aneurysms, arteriovenous malformation, and uterine fibroids and to reduce blood flow to solid tumors including liver tumors. Embolization may be achieved by any number of means, including through the use of polymer microspheres, metal coils or plugs and liquid embolic materials.
In a typical embolization procedure, local anesthesia is first given over a common artery or vein. The artery or vein is then punctured and a catheter is inserted and fluoroscopically guided into the area of interest. An angiogram is performed by injecting contrast agent through the catheter, thereby visualizing the portion of the vascular tree downstream of the distal end of the catheter. Once the catheter is positioned in a site where deposition of an embolic agent is desired, the composition or agent is deposited through the catheter. The embolic agent is generally selected based on the size of the vessel to be occluded, the desired duration of occlusion, and/or the type of disease or condition to be treated, among others factors. Following delivery of the embolic agent to the site within the vessel to be occluded, a follow-up angiogram can be performed to determine the specificity and completeness of the occlusion.
In many common embolic procedures, including sandwich embolization of splancnic aneurysms, sandwich embolization of gastrointestinal bleeds, embolization of vessels to treat varioceles or pelvic congestion syndrome, and embolization to arrest hemorrhage after trauma, embolization is desired along of a length of blood vessel, rather than at a focal point. However, embolic coils, which are most commonly used in embolization procedures, are optimally used in focal embolization applications. In practice, users may use multiple embolic coils to pack and fill the length of the vessel, but this approach is time- and material-intensive, as many coils must each be placed individually, increasing the costs of such procedures.
Liquid and swellable embolics have recently emerged as a potential alternative to coil-packing procedures. Throughout this disclosure, the terms “liquid embolics,” “gel embolics” and “swellable embolics” are used interchangeably to refer to (a) flowable polymerizing embolic materials, which include TRUFILL® n-Butyl Cyanoacrylate (n-BCA) (Codman & Shurtleff, Inc., Raynham, Mass.) and ONYX® ethylene vinyl alcohol copolymer (EVOH) (ev3 Endovascular, Inc., Plymouth, Minn.), as well as (b) absorbent or superabsorbent polymer embolics, such as collagen occlusive plugs These materials can be expensive (up to $2,500 per mL in the case of EVOH embolics) and, when deployed in vessels with relatively high flow rates, may be prone to migration and embolization of non-target areas. To prevent such migration, practitioners may deploy coils on the proximal and/or distal ends of a region being embolized, in order to reduce blood flow thereto. This approach, however, also requires multiple steps, and may require the use of multiple catheters, particularly when using liquid embolics (such as n-BCA) solidify within the catheter, necessitating the placement of a new catheter if deployment of an embolic coil proximal to the already polymerized embolic mass is desired.
Another alternative to packing vessels with conventional embolic coils and/or liquid embolics is to use multiple hydrogel-coated embolic coils, such as the AZUR™ coil (Terumo Medical Corporation, Somerset, N.J.); these coils expand radially when exposed to aqueous environments, allowing them to occupy more space than conventional embolic coils having an equivalent pre-deployment diameter. Even so, procedures involving these devices will typically require placement of multiple coils, and will thus involve greater complexity and expense than interventions which require only a single deployment step.